Thanks for the question. Were these songs purchased from the iTunes Store? If so, see the following resource. If not, follow the same steps for the content, based on how you acquired it (delete and re-add).
Occasionally, if a song purchased from the iTunes Store on a Mac or PC was not downloaded completely, the song may not play back fully. The song may abruptly stop during playback, and iTunes may start playing the next song in your library or playlist.
If iTunes in the Cloud is available in your country, try the following steps to resolve the issue:
1. Delete the purchased song that is exhibiting the problem from your iTunes library.
2. Click on the Purchased link in the iTunes Store to view your previously purchased music.
3. Download your previously purchased song from this list.
Note: iTunes in the Cloud, which allows you to download previously purchased songs from the iTunes Store, is not available in every country. Learn if iTunes in the Cloud is offered in your country.
a lot of people have quite the same problem (including me).
It concerns all the recently added files in your library.
You can find some other comments here but no solutions for the moment :
I confirm that this is VERY annoying. I've already send a bug report to Apple 2 weeks ago.
Maybe you noticed that all your added song just skip at the same exact time ?